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Variable interest entities (Details) (USD $) | Dec. 31, 2013
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Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Percent of ownership | 50.00%
Total project costs | $ 300,000,000
Portion of capital commitment | 150,000,000
Partner portion of capital commitment | 75,000,000
Excess capital commitments | 300,000,000
Estimated project cost | 350,000,000
Term loan for project debt financing | 75,000,000
Fuel contract [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount | 7,700,000
Cash and Cash Equivalents [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Assets | 4,774,000
Other Current Assets [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Assets | 26,000
Total current assets [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Assets | 4,800,000
Net property, plant and equipment [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Assets | 172,073,000
Total assets [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Assets | 176,873,000
Long-term debt due within one year [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | 3,000,000
Accounts payable [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | 8,904,000
Taxes payable [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | 5,000
Accrued compensation [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | 26,000
Other accrued liabilities [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | 461,000
Total current liabilities [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | 12,396,000
Long-term debt [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | 72,000,000
Total liabilities [Member] | Dakota Prairie Refining, LLC [Member] |
Variable Interest Entities [Line Items] |
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | $ 84,396,000

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- Definition Excess capital commitments above this amount will be shared equally. + References No definition available. + Details
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Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Partner portion of capital commitment. + References No definition available. + Details
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Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Percent of ownership. + References No definition available. + Details
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- Definition Portion of capital commitment. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Project cost estimate + References No definition available. + Details
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Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of term loan entered into to finance the project. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Total project costs. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685 + Details
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- Definition The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685 + Details
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- Definition The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph b -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5728-111685 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5747-111685 + Details
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- Details
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